>>"can i plug my Vista into the second ISP port on the dual WAN router and use its wireless card to access the internet for all users."
Yes. So long as ICS (internet connection sharing) is enabled on the Vista machine. The second wan port will get an address using DHCP from the Vista machine which will include the DNS entries.
>>"No further action required."
Correct, however I would be tempted to add the DNS server IP's associated with the wireless card to the SBS DNS forwarders. I can't recall back to SBS 2000 but it should be found by opening the DNS management console, expand your domain, and in the right hand window you should see forwarders (not forward lookup zone). Just add those DNS servers to the bottom of the list. They can remain present at all times.
>>"the router would take care of the switching automatically?"
It should if it is a dual WAN router. What model is it? The one issue you can run into with dual WAN routers is they may have load balancing enabled by default. If this is the case the first user to connect to an Internet services uses WAN port 1, the second WAN port 2 and so on. If the second port has a lower bandwidth that the first users will see reduced performance. Some dual WAN routers allow you to disable load balancing and just use fail-over protection. If yours doesn't have that option you can disconnect the Vista machine and plug it in when necessary.
